This invention relates generally to an apparatus and a method for spray coating discrete particles while the particles are suspended in a fluidized bed. More particularly, the present invention relates to an apparatus and a method of coating particles in an upward flowing fluidized bed dryer having an insert comprising a vertically adjustable cylindrical partition and a vertically adjustable spray nozzle.
The application of fluid bed technology for coating particles and forming agglomerates is well known in the art. Glatt Air Techniques, Inc. located in Ramsey, N.J., Vector Corporation located in Marion, Iowa, and Niro, Inc. located in Columbia, Md., the manufacturer of the Aeromatic dryer are three suppliers of batch type fluid bed dryers wherein the present invention is utilized. The batch fluid dryers are typically used in the pharmaceutical, polymer, food, and nutriceutical industries.
It is well known in the art to coat particles using a co-flow spray system in which the liquid droplets and the particles are both flowing in an upwardly direction. A patent to D. E. Wurster (U.S. Pat. No. 3,089,824) discloses a dryer in which the particles and liquid are flowing in the same upwardly direction. Additionally, the Wurster patent discloses a spray nozzle which is in contact with a mesh screen located at the bottom of the dryer. A patent to H. W. Mesnard et al. (U.S. Pat. No. 2,986,475) discloses a co-flowing dryer in which fluidizing gas is injected into the system in the center of the dryer while the liquid spray nozzle is positioned through the side of the dryer. Additionally, a patent to A. L. Heiser (U.S. Pat. No. 3,112,220) discloses an upward flowing fluidized bed dryer where the particles and the atomized liquid are flowing in the same upwardly direction. The Heiser patent also discloses a spray system with a dedicated liquid handling system. Uniform coating is difficult to achieve using the methods and dryer systems of any of these patents.
The next advancement in the coating of particles was to create a dedicated coating chamber and coating zone by the use of a partition within the dryer as disclosed in the patent to Wurster et al. (U.S. Pat. No. 3,241,520). Additionally, the Wurster et al. patent discloses, besides the dedicated coating zone, a subsident coating area or a reconditioning zone. Furthermore, the Wurster et al. patent discloses the spray nozzle being attached to the bottom screen.
A patent to G. W. Larson et al. (U.S. Pat. No. 3,110,626) discloses an upward flowing fluidized bed dryer with a dedicated coating zone by the use of a partition. Additionally, this patent discloses an atomizing nozzle which is mounted to a bottom screen.
A patent to Debayeux et al. (U.S. Pat. No. 4,335,676) discloses a spouted bed granulator and/or coating apparatus. The Debayeux et al. patent describes a process for coating particles in which the gas flow directing structure prevents contact and agglomeration of particles in the vicinity of the walls of the dryer. The flow in the apparatus disclosed in the Debayeux et al. patent provides a gaseous stream in an upward direction which allows the liquid spray nozzle to better coat the particles. The improved process is accomplished by reducing the diameter of the air duct around the spray nozzle.
A patent to Mutsers et al. (U.S. Pat. No. 4,701,353) discloses a spraying device in an upward flowing fluid bed dryer in which the liquid is sprayed with a gas creating a conical film. The resulting conical film spray pattern is not protected about its initial base by an upwardly moving column of gas. Additionally, the spray device is connected to the bottom plate of a spray dryer.
A patent to Maag et al. (U.S. Pat. No. 4,960,244) discloses an atomizing nozzle with constricted liquid tubes. The constricted liquid tubes eliminate the need for metering pumps or flow meters for each atomizing nozzle to control the flow of liquid through the spray nozzle.
A patent to Wurster (U.S. Pat. No. 3,196,827) discloses an upward flowing fluidized bed dryer with a fixed cylindrical partition which creates a dedicated coating zone. Additionally, the Wurster patent discloses a spray nozzle positioned below the cylindrical partition which is fixed to the air distribution screen on the bottom of the dryer. Finally, the Wurster patent discloses a cyclical process in which particles are coated in the coating zone and are carried through the coating zone with the fluidizing gas. Once the gas and particle velocities decrease when the particles leave the coating zone, the particles fall through the reconditioning zone and into the fluidized bed. The coated particles in the particle bed are pulled into the coating zone by a draft created by the upward flow of atomizing gas from the spray nozzle, after which the coating process is repeated.
A patent to David M. Jones (U.S. Pat. No. 5,437,889) discloses an adjustable cylindrical shield for the spray nozzle. The Jones patent discloses the purpose for the adjustable cylindrical shield for the spray nozzle is to control the entrance of particles into the spray pattern. The Jones patent further discloses that the controlled entrance of particles into the coating zone improves the liquid droplet pattern which in turn improves the coating quality of the process. Furthermore, the Jones patent discloses that the spray nozzle is mounted to the bottom atomizing air screen.
A patent to Littman et al. (U.S. Pat. No. 5,254,168) discloses a dual jet coating design. The coating spray is applied both upward and downward within a coating zone in which the cylindrical partition is adjustable within the coating zone. However, the bottom spray device is fixed onto the machine body. Additionally, the Littman patent discloses an adjustable spray nozzle that is adjustably positioned through the bottom fluidizing air screen, and the fluidizing air screen contains an aperture through which the spray nozzle is adjusted.